1. Field of the Invention
The present invention relates to a power amplifying apparatus and method using pre-distortion and a radio communication system including the same power amplifying apparatus.
2. Related Prior Art
To design a power amplifier it is required to consider both the signal distortion characteristic and the amplification factor because the two factors are inconsistent with each other. For example, an A-grade amplifier barely has signal distortion while having a low amplification factor. The C-grade amplifier has severe signal distortion while having a high amplification factor.
Recently, a variety of attempts to increase the amplification factor without causing signal distortion have been made. Pre-distortion is a typical method for increasing the amplification factor. The pre-distortion method intentionally distorts a signal input to a power amplifier before the signal is applied to the power amplifier to compensate for the nonlinear characteristic of the power amplifier. The pre-distortion method distorts the input signal according to a pre-distortion function to achieve linearization, thus satisfying high efficiency and low distortion characteristics. The pre-distortion function has a characteristic opposite to the characteristic function of the power amplifier.
FIG. 1 is a block diagram of a conventional typical pre-distortion system. Referring to FIG. 1, a digital baseband input signal Un is inputted to a pre-distortion module 20 and pre-distorted according to a pre-distortion function A(.) to be outputted as Xn. The signal Xn is converted to an analog signal by a D/A converter 30. The analog signal is converted to an RF signal by an up-conversion module 40 consisting of a mixer and a filter, and it is inputted to a power amplifier 50 to be amplified.
The conventional pre-distortion method is carried out through two steps. First, the characteristic of the power amplifier 50 is produced, and then the pre-distortion function A(.) is obtained on the basis of the characteristic of the power amplifier. To produce the characteristic of the power amplifier 50, the input and output signals of the power amplifier should be compared to each other. Accordingly, the output signal of the power amplifier 50 is fed back and inputted to a down-conversion module, consisting of a mixer and a filter, to be converted to an intermediate frequency (IF) signal. The IF signal is converted to a digital baseband signal yn by an A/D converter 80. The signals Xn and yn are inputted to an amplifier characteristic producing module 25, and the characteristic function of the power amplifier 50 is produced on the basis of the signals Xn and Yn. A pre-distortion function decision module 15 determines the pre-distortion function A(.) on the basis of the characteristic function of the power amplifier 50, which is produced by the amplifier characteristic producing module 25. The pre-distortion module 20 pre-distorts the input signal un according to the pre-distortion function A(.).
The aforementioned conventional pre-distortion system carries out the two steps of producing the characteristic function of the power amplifier 50 and of deciding the pre-distortion function on the basis of the characteristic function. Thus, hardware complexity of the pre-distortion system is increased and probability of linearization error in the pre-distortion system is also increased.